Hands down the Sheraton. They have the Ohana (family) suites to which they upgrade Plats to unless they are completely full and the Westin rarely upgrades and even if they do it's only to a location (like Ocean front) but the rooms are small and outdated even if they have killer views or proximity to the ocean. I also got an Exec Suite one time up on Black Rock that was huge. It wasn't the greatest location but it was a massive suite.

Also I do believe you are allowed to go use the pools at the Westin Hotel as well as the Resort Villas (there's a shuttle). And The Resort Villas has great family-friendly pool stuff for young families like the pirate ship kiddie pool area.